Constant voltage regulator dependent on resistor ratios



United States Patent 01 lice 3,416,067. Patented Dec. 10, 1968 3,416,067CONSTANT VOLTAGE REGULATOR DEPENDENT ON RESISTOR RATIOS Leander H. Hoke,In, Southampton, Pa., assignor to Philco-Ford Corporation, Philadelphia,Pa., a corporation of Delaware Filed Nov. 9, 1966, Ser. No. 593,122 5Claims. (Cl. 323-17) This invention relates to an electronic regulatorcircuit and more particularly to a novel semiconductor amplifier circuitespecially suitable for use as a voltage regulator circuit.

Conventional voltage regulator circuits contain a voltage referencedevice and usually compare a fraction of the potential at the outputterminal of the circuit with a reference potential supplied by thevoltage reference device. The voltage reference device is usually aZener diode, a glow tube, or a battery. Although glow tubes andbatteries may be suitable for use in conventional voltage regulatorcircuits, they are obviously unacceptable for use With integratedsemiconductor circuits.

It has been found that the Zener breakdown voltage of a diode dependsupon the pattern of the concentrations of impurities in the proximity ofthe p-n junction. Since it is very difficult to determine or control thepattern of impurity concentration in the proximity of a p-n junction inan integrated semiconductor circuit it is difiicult to manufacture Zenerdiodes having preselected characteristics as part of an integratedcircuit. Therefore, Zener diodes are not suitable voltage references inintegrated semiconductor circuits.

Zener diodes are also undesirable as components of integratedsemiconductor circuits because the Zener potential of the diodes isfunctionally related to temperature. A rise in temperature of a Zenerdiode is accompanied by a rise in the Zener breakdown potential of thediode. It is very difiicult to compensate for this temperature variationbecause the relationship between the Zener potential of a diode and thetemperature of the diode is a nonlinear function.

It is therefore an object of the present invention to provide animproved voltage regulator circuit.

Another object is to provide a voltage regulator circuit which does notrequire a voltage reference device.

Another object is to provide a voltage regulator circuit that can befabricated as a single integrated circuit.

An additional object is to provide a circuit in which the output voltagecan be caused to increase, decrease or remain constant in amplitude withchanges in input or supply voltage.

According to the present invention the voltage regulator circuitcomprises only resistors and transistors. The output voltage of thecircuit is maintained at a constant amplitude independent of the valueof the input voltage by proper choice of the ratio of values of theresistors of the circuit.

In a specific embodiment of the present invention the circuit comprisesfirst and second supply terminals to which a voltage is supplied, firstand second amplifier circuits connected across the supply terminals, avoltage divider connecting a terminal of the first amplifier circuit tothe second supply terminal, and first and second load impedancesconnecting first and second terminals of the second amplifier circuit tothe first and second supply terminals. A control terminal of the firstamplifier circuit is connected to the first terminal of the secondamplifier circuit and a control terminal of the second amplifier circuitis connected to a tap on the voltage divider and to the first supplyterminal.

The above objects and other objects inherent to the present inventionwill be more clearly understood when reference is had to theaccompanying drawing, in which:

FIG. 1 is a schematic diagram of the circuit of the present invention;

FIG. 2 is a graph showing the transfer characteristics of the circuit ofFIG. 1;

FIG. 3 is a schematic diagram of the circuit of the present inventionused as a variable attenuation circuit; and

FIG. 4 is a graph showing the transfer characteristics of the circuit ofFIG. 3.

Referring to FJG. 1, the positive terminal of a directcurrent voltagesource V is connected to the collector or output electrode of a firsttransistor T through a resistor R to the base or control electrode of asecond transistor T and through a resistor R to the collector or outputelectrode of said second transistor T By way of example, the transistorsT and T are shown to be of the N-P-N type although the circuit can bereadily modified to employ transistors of the P-N-P type. The baseelectrode of the first transistor T is connected to the collectorelectrode of the second transistor T and through said resistor R to thedirectcurrent voltage source V The emitter electrode of the firsttransistor T is connected through a voltage divider network 8 whichcomprises serially conected resistors R and R to a point of referencepotential, for example, ground. The junction point 10 of the resistors Rand R is connected to the base electrode of the transistor T The emitteror common electrode of the second transistor T is connected through aresistor R to the point of reference potential. The regulated outputvoltage V appears across the voltage divider network 8, which may beconnected in parallel with any load device (not shown) that requires aconstant amplitude supply voltage.

In accordance with the present invention, I have discovered that properselection of the value of the resistor R will make the output voltage Vindependent of the amplitude of the supply voltage V for amplitudes ofthe supply voltage greater than a minimum value. It is to be noted thatthe regulated output voltage V is achieved without the incorporation ofa voltage reference device in the circuit.

Referring now to FIG. 2, there is shown a graph of the transfercharacteristics of the circuit of FIG. 1 for different values of theresistor R It can be seen that for a critical value R of the resistor Rthe output voltage V remains constant for a large range of amplitudes ofthe supply voltage V greater than a minimum value V For values of theresistor R above and below the critical value R the value of the outputvoltage V,. increases or decreases when the amplitude of the supplyvoltage changes.

Referring again to FIG. 1, the equation for computing the critical valueR of the resistor R may be derived as follows. For the purpose of thisderivation, it is assumed that the value of alpha for the transistors Tand T is equal to unity, hence base current in the transistors T and Tis considered negligible compared to collector and emitter currents inthese transistors. It is also assumed that the internal resistances oftransistors T and T are negligible.

Analysis of FIG. 1 shows that the independent variable V and thedependent variable V are equated to the branch currents I and I and tothe resistances R R R and R according to the equations and substitutingEquations 5, 6, and 7 into Equation 8, Equation 8 becomes Equation 9 canbe expanded to the form R2 RiR 1 a 1 V I: R3 (R1+1a:5 Rt+R5 -R5 R2 VI:119

The value of R which satisfies Equation 10a, heretofore referred to as Rprovides a voltage regulator circuit in which the output voltage V isindependent of the supply voltage V The value of the regulated outputvoltage V when R equals R is determined by noting the constraints on theresistance values given by Equation 10a and substituting these valuesinto Equation 9a. This substitution yields If the transistors T and Tare assumed to have matched base-emitter voltages V and V respectively,at their respective current levels, and these voltages are both referredto as V a simplification of Equation 11 is possible and thesimplification yields Vbe i 1) R30 From the foregoing explanations andfrom an analysis of Equation 12, it is readily apparent that the circuitof the present invention will produce an output Voltage V which isindependent of the magnitude of the supply voltage V Furthermore, theform of the Equations 10a and 12 show that the regulationcharacteristics of the circuit are dependent upon resistor ratios ratherthan absolute values. Since resistance ratios are easily controlled inthe manufacture of integrated circuits by controlling ratios of areas,the circuit of the present invention is ideal for use in integratedcircuits.

Equations for the values of R and V for values of alpha other than unityand internal transistor resistances other than zero can be derived in asimilar manner. However, this added precision results in an equation ofconsiderable complexity. In practice, it is sufiicient to select theapproximately correct values of the circuit parameters in accordancewith Equations 10a and 12 and then, if greater precision is required,determine experimentally the precise values required to give a constantoutput voltage of the desired value V The operation of the system of thepresent invention can also be explained as follows. If the supplyvoltage V is either increased or decreased, this change tends to appearat the load and also across the voltage divider network 8 formed by theresistors R and R The change in voltage across the voltage dividernetwork 8 is detected at the base of transistor T thereby changing thecollector current of transistor T either increasing or decreasing thiscurrent. This changes the current through resistor R and a change in thecollector to base bias of the transistor T results. The latter changeadjusts the magnitude of the collector to emitter current flow oftransistor T to maintain a constant voltage V across the load device(not shown).

A variable value of regulated voltage is achieved by replacing theresistors R and R by a potentiometer. When the wiper arm of thepotentiometer is near the center of the potentiometer range and thevalue of resistor R is in accordance with Equation 10a, the value of theoutput voltage V can be varied over greater than a two to one range withsmall changes in the position of the wiper arm. The voltage variation isachieved with only a minor loss of regulation.

It is well known that the gain of the usual transistor amplifier stagechanges with temperature. This is mainly due to the fact that theparameter V changes with temperature. This variation in gain of thetransistor stage can be offset by an appropriate change in the collectorbias voltage. The voltage regulator circuit of the present inventionproduces an output voltage which is a direct function of the transistorparameter V (Equation 12) and thereby offers the advantage of providinga collector supply voltage which changes automatically in the correctdirection to compensate for any change in gain of a transistor stageconnected thereto which undergoes the same temperature change as theregulator circuit.

In a specific embodiment of the present invention which has provensuccessful as a voltage regulator in a transistor radio receiver, thevalues of the resistors R R and R were each 10,000 ohms and the initialsupply voltage was a 6 volt battery. The value of resistor R was 1,090ohms and the value of resistor R was 725 ohms. The discrepancy in thevalue of the resistor R from the value (@900 ohms) computed usingEquation 10a is due to the assumptions that the internal resistances ofthe transistors T and T are negligible and that the base currents of thetransistors T and T are negligible compared to collector and emittercurrents of these transistors. In this embodiment, the output voltage Vremained constant at 3 volts even though the supply voltage V decreaseddue to discharging of the 6 volt battery.

The system of the present invention is also useful as a variableattenuation circuit. Referring to FIG. 3, which shows the circuit ofFIG. 1 redrawn with the input and output terminals designated e (t) and(2 (1), respectively, to denote the A.C. input and output signals of thecircuit, respectively. FIG. 4, which is similar to FIG. 2, shOWs thetransfer characteristics of the circuit of FIG. 3 and shows that theamplification of the input signal, e (t), produced by the circuit ofFIG. 3 is dependent upon the value of the resistor R If the value of theresistor R is equal to R the circuit will remove AC signal variations ofany signal having a DC bias V greater than the critical level V by thepeak amplitude of the AC component and will produce a controlled DCoutput signal, thus, acting as a regulator. If the value of R is greaterthan R an output signal having the same phase as that of the inputsignal will be produced, the amplitude of this signal being dependent onthe difference between the value of R and R Similarly if the value of Ris less than that of R the output signal will have an amplitudedependent on the difference between the value R and that of R However,in this instance, the phase of the output signal will be opposite tothat of the input signal. Due to the linearity of the transfer impedanceof the circuit of FIG. 3, the circuit can control much larger signallevels than conventional transistor gain control circuits whileintroducing very little distortion.

While the invention has been described with reference to certainpreferred embodiments thereof, it will be apparent that variousmodifications and other embodiments thereof will occur to those skilledin the art within the scope of the invention. Accordingly I desire thescope of my invention be limited only by the appended claims.

I claim:

1. A circuit comprising first and second supply terminals to which avoltage may be supplied; a first series circuit connected between saidfirst and second supply terminals and comprising a first amplifierelement having first and second terminals of a main current path and acontrol terminal for controlling current flowing in said main currentpath,- and a voltage divider connecting said second terminal of saidfirst amplifier element to said second supply terminal; a second seriescircuit connected between said first and second supply terminals andcomprising a second amplifier element having first and second terminalsof a main current path and a control terminal for controlling currentflow in said main current path, and first and second load impedancesconnecting said first and second terminals, respectively, of said secondamplifying element to said first and second supply terminals,respectively; means connecting said control terminal of said firstamplifier element to said first terminal of said second amplifyingelement, means connecting said control terminal of said second amplifierelement to an intermediate tap on said voltage divider, and meansconnecting said control terminal of said second amplifier element tosaid first supply terminal.

2. The circuit of claim 1 in which said last-mentioned means includes aresistor R said first and second load impedances are resistors R and Rrespectively, and said voltage divider network comprises two resistors Rand R connected in series.

3. The circuit of claim 2. in which said resistor R has a valueapproximately equal to the value determined by the formula 4. Thecircuit of claim 3 in which said first and second amplifier elements aretransistors, in which said first, second, and control terminals arecollector, emitter, and base electrodes, respectively.

5. A voltage regulated power supply circuit comprising only: a voltagesource, a first transistor and first and second resistors connected in afirst series circuit across said voltage source, a second transistor andthird and fourth resistors connected in a second series circuit acrosssaid voltage source, a direct connection from the control electrode ofsaid first transistor to an intermediate point on said second seriescircuit, a direct connection from the control electrode of said secondtransistor to an intermediate point on said first series circuit, and afifth resistor connected between one of said control electrodes and oneterminal of said voltage source.

References Cited UNITED STATES PATENTS 2,991,407 7/1961 Murphy 323-43,141,135 7/1964 Amlinger et al. 307-303 X 3,142,021 7/1964 Stelmak 307303 X 3,223,781 12/1965 Hestad 323-22 X 3,246,233 4/1966 Herz 323 43,271,685 9/1966 Husher 61; al. 307 303 X LEE T. HIX, Primary Examiner.A. D. PELLINEN, Assistant Examiner.

US. Cl. X.R.

5. A VOLTAGE REGULATED POWER SUPPLY CIRCUIT COMPRISING ONLY: A VOLTAGESOURCE, A FIRST TRANSISTOR AND FIRST AND SECOND RESISTORS CONNECTED IN AFIRST SERIES CIRCUIT ACROSS SAID VOLTAGE SOURCE, A SECOND TRANSISTOR ANDTHIRD AND FOURTH RESISTORS CONNECTED IN A SECOND SERIES CIRCUIT ACROSSSAID VOLTAGE SOURCE, A DIRECT CONNECTION FROM THE CONTROL ELECTRODE OFSAID FIRST TRANSISTOR OT AN INTERMEDIATE POINT ON SAID SECOND SERIESCIRCUIT, A DIRECT CONNECTION FROM THE CONTROL ELECTRODE OF SAID SECONDTRANSISTOR TO AN INTERMEDIATE POINT ON SAID FIRST SERIES CIRCUIT, AND AFIFTH RESISTOR CONNECTED BETWEEN ONE OF SAID CONTROL ELECTRODES AND ONETERMINAL OF SAID VOLTAGE SOURCE.